Assemblies comprising electronic elements such as flexible, partially flexible or rigid electronic circuits or integrated circuits which are positioned in a recess of a polymeric carrier substrate such as a polymeric card, are widely used, for example, in the form of credit cards, cash cards, smart cards, telephone cards or identification cards such as radio frequency identification (RFID) tags. The electronic carrier elements have been bonded to the polymeric carrier substrate by means of structural adhesives which are desired for high bond strength and tamper resistance, but which are usually brittle and do not provide the durability and flexibility required during usage of credit cards, smart cards and similar assemblies.
A heat-activatable adhesive film for use with a data storage medium has been described with an integrated circuit element arranged in a recess of the body of a card. The exemplified film comprises nitrile rubber, phenolic resin and zinc oxide. This adhesive resin tends to be too brittle and not sufficiently flexible for many applications.
An electronically conductive, thermoplastic and heat-activatable adhesive sheet has been described to contain a thermoplastic polymer in a proportion of at least 30 weight percent (wt. %), one or more tackifying resins in a proportion from 5-50 wt. %, and/or epoxy resins with hardeners in a proportion of from 5-40 wt. %, as well as metalized particles in a proportion of from 0.1-40 wt %, and from 1-10 wt. % non-deformable or virtually non-deformable spacer particles. The exemplified adhesive sheet contains nitrile rubber, phenolic resin, glass beads and gold-coated polystyrene beads.
Also known are electrically conductive, thermoplastic and heat-activatable adhesive films. Such known heat-activatable adhesive films tend not to be sufficiently flexible for demanding applications such as credit cards, identification cards, or smart cards.